Tunable millimeter wave band pass filter using electromagnetic crystal sidewalls

Electromagnetic crystal (EMXT) structures are used as the waveguide sidewalls of a Ka-band waveguide cavity. With InP heterobarrier varactors (HBV) embedded, the EMXT structure acts as an electronically tunable surface impedance in place of the normal conducting metal sidewalls. By controlling and varying the sidewall impedance with a dc voltage, the EMXT waveguide propagation constant is varied and the effective electrical length of the cavity changed. The center of the pass band was tuned 31.6 GHz by varying the varactor bias from 0 to 10V. It is demonstrated that the guide width can play a significant role in controlling tuning range. Good agreement between measured and simulated band pass response was obtained.